"I just don't think that it's a wise move," the Arizona Republican said in an interview on "The Lead with Jake Tapper," reacting to the President's announcement earlier in the day that the US will withdraw from the nuclear agreement. "Our allies and our adversaries need to know that we are reliable, and I think that's missing right now."

The deal, signed in 2015 between Iran, the US and other major world powers, including France and the United Kingdom, eased economic sanctions on Iran in exchange for curbs on its nuclear program.

On Tuesday, Trump called the agreement "decaying" and "rotten" and said, "It is clear to me that we cannot prevent an Iranian nuclear bomb" under the terms of the deal.

Flake warned, however, that "what we've done now is we've given Iran license basically to get out, if they choose, of their nuclear obligations."

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When Tapper asked if the US will be more or less safe now, the senator said, "I don't think that we're more safe. I agree with what Gen. Mattis said ... that we should stay in the agreement," referring to Secretary of Defense James Mattis.

The senator added that he has concerns that Trump's decision to quit the Iran deal may endanger other US diplomatic efforts.

"A lot of experts have talked about the knock-on aspects of this, what it will mean for other agreements," Flake said. "If the North Koreans say, 'Well, hey, they only stayed within this agreement for a couple of years,' then they'll be more reluctant to sign on the dotted line, in particular to do what we're wanting them to do, and that's denuclearize."

The senator, a member of the Senate Foreign Relations Committee, came out against the Iran deal in 2015. At the time, he said the agreement imposed "severe limitations" on "Congress and future administrations in responding to Iran's non-nuclear behavior in the region."

On Tuesday, Flake was quick to criticize the Obama administration's approach to the deal as well.

"It certainly could have been a better deal and it should have been structured differently," Flake said. "President Obama should have come to the Senate and proposed it as a treaty and we wouldn't be going through what we're going through now, and I think it would have been a much better deal."